Tajikistan and the other Central Asian Republics are experiencing HIV epidemics that are driven by injecting drug use. The proposed 3-year R34 project will pilot test the feasibility of a structural intervention to switch needle and syringe program (NSP) clients in Tajikistan from high dead space to low dead space needles and syringes. Circumstantial evidence from laboratory experiments, biobehavioral surveys, ecological studies, and mathematical models suggests that such an intervention could substantially reduce HIV transmission among people who inject drugs (PWID). In mathematical models, such an intervention would prevent injection- related HIV epidemics among PWID from occurring in the first place and reverse injection-related epidemics that have occurred. However, no one knows whether such an intervention is feasible or whether it would actually reduce HIV incidence. The proposed project will use a combination prevention approach that works with NSP (structural intervention) to distribute low dead space needles and syringes (biomedical device/intervention). Our efforts to promote the adoption and diffusion of low dead space needles and syringes will be informed by Diffusion of Innovations Theory. Findings from the study will determine whether it makes sense to design and implement an expensive randomized controlled trial (RCT) with HIV incidence as an outcome to test such an intervention. The proposed pilot test will be conducted at two NSP that are located in Kulyob and Khorog, Tajikistan. These NSP distribute only high dead space needles and syringes. HIV prevalence among PWID is 24% in Kulyob and 14% in Khorog. The specific aims of the proposed study are as follows: Aim 1. To pilot test the feasibility of a structural intervention to switch NSP client in Tajikistan from high dead space to low dead space needles and syringes. Aim 2. To evaluate the potential impact of such an intervention by incorporating findings from the pilot test into ou predictive mathematical model of the effects of syringe type on HIV transmission among PWID. If we find that the intervention is feasible and the model suggests that it would have substantial impact, we will design a full RCT to test the intervention using HIV incidence as an outcome.